1. Technical Field
This invention relates to masking materials and to their use during the application of two or more coating materials to a surface. In particular the invention relates to masking materials having a curved edge strip which is removable from the remainder of the masking material.
2. Description of the Related Art
Masking foam tape comprising a foam substrate having on part of its outer surface a layer of pressure-sensitive adhesive is known. A preferred tape has a cross-section comprising a curved surface e.g., circular or elliptical, since such masking tape allows a xe2x80x9cfeathered edgexe2x80x9d or xe2x80x9csoft edgexe2x80x9d, to be attained during surface coating operations, such as painting. The masking tape is positioned such that the curved surface overhangs the surface to be painted and thus when the paint is sprayed only paint projected at certain angles will pass beneath the overhanging portion of the masking tape and the paint thickness will be thinner, the edges beneath the overhang allowing a smooth transition to the adjacent painted area to be attained. The use of foam allows paint impinging thereon to be absorbed preventing it running off the masking material and marring the surface being treated. Such masking material is commercially available from 3M United Kingdom plc under the trade name Soft Edge Masking Foam Tape.
Soft edge masking foam tape (SEMFT) may be produced from a foam web by compression over a predetermined area with a blunt rotary cutter so that a cold-welded seam is formed which secures opposing surfaces of the web to each other at the region of the weld, thereby forming a curved surface. An array of circular or elliptical adjacent foam strips which are readily separable may be formed by passing a foam web through a plurality of parallel blunt rotary cutters causing compression and welding of the foam along parallel lines. The production of such foam strips is disclosed in EP-B-0384626. Other masking materials comprising foam, which may be cold-welded are disclosed in GB-2254811 and GB-2288137.
SEMFT is commonly used to mask the inside of door apertures to prevent paint or primer spray from contaminating the inside of the vehicle. After applying primer to a car panel it is desirable to apply the paint in a manner such that it extends beyond the primer to ensure the primer is completely covered and not left exposed. In such situations the SEMFT may be removed after application of the primer and repositioned. Alternatively, the SEMFT may be gently pushed in an attempt to displace it and position it away from the primer edge. Neither technique is satisfactory since it is labour intensive and not desirable if the primer is still wet.
The invention has been made with this point in mind.
According to one aspect of the invention there is provided a masking material comprising an elongate strip at least partially coated with a layer of a pressure-sensitive adhesive. The strip has a curved surface which is convex when the strip is viewed in cross-section and is positioned such that when the strip is adhered to a substrate by the layer of pressure-sensitive adhesive a portion of the curved surface overhangs the substrate. The masking material comprises a removable edge portion comprising the portion of the curved surface detachably secured to a remainder of the strip and which may be removed to expose a second curved surface on the remainder of the strip which is convex when viewed in cross-section and which is positioned to overhang the substrate. The removable portion and the remainder of the strip have different dimensions.
According to a second aspect of the invention there is provided a method of coating an area of the surface of a substrate with layers of a first and second coating material. The method comprises the steps of:
(i) Providing a masking material comprising an elongate or endless strip at least partially coated with a layer of a pressure-sensitive adhesive. The strip has a curved surface which is convex when the strip is viewed in cross-section and is positioned such that when the strip is adhered to a substrate by the layer of pressure-sensitive adhesive a portion of the curved surface overhangs the substrate. The masking material comprises a removable edge portion comprising the portion of the curved surface detachably secured to the remainder of the strip and which may be removed to expose a second curved surface on the remainder of the strip which is convex when viewed in cross-section and which is positioned to overhang the substrate. The removable portion and the remainder of the strip have different dimensions.
(ii) Applying the masking material to the substrate such that the curved surface is adjacent the edge of the area to be coated.
(iii) Applying the first coating material over the area of the surface up to the masking material.
(iv) Detaching and removing the removable portion of the masking material.
(v) Applying the second coating material over the first coating material and up to the remainder of the masking material.
The masking material of the invention is simple and effective to use. The elongate strip is applied to the surface in the normal manner with the curved surface adjacent the edge of the area of the surface to be coated. After application of a first coating material, e.g., primer, the curved surface is readily removable to expose a second curved surface slightly extending the area to be coated such that the second coating will completely overlap the first coating while ensuring a feathered edge is obtained. Thus, repositioning of the masking material between successive coating operations is unnecessary.
The masking material is preferably made of foam and may conveniently be produced by cold-welding foam web by the techniques disclosed in EP-0384626. Polyurethane foam is preferred for use in the cold-welded embodiments of the invention. The foam preferably has a density of about 26 Kg/m3. A preferred cold-weldable foam is commercially available from Caligen Foam Limited under the trade designation xe2x80x9cGrade 4273Axe2x80x9d.
The removable edge of the masking material may be achieved in various ways.
In one embodiment, the elongate strip may be formed with a circular or elliptical cross-section and a layer of foam or similar material releasably secured to and following the contour of the curved surface extends as a strip along the length of the masking material to form a removable edge. The removable strip may be secured by pressure-sensitive adhesive, welding or a combination thereof.
Such a masking material may be made by a method which comprises the steps of:
(a) providing a first cold-weldable foam web;
(b) applying at least two parallel stripes of a pressure-sensitive adhesive to a surface of the foam web;
(c) applying a second cold-weldable foam web having a thickness less than that of the first web to the first web such that the second web overlaps but does not completely cover the adjacent parallel stripes of pressure-sensitive adhesive;
(d) compressing the first and second cold-weldable webs midway between the adjacent stripes of pressure-sensitive adhesive using a blunt rotary cutter so that a cold-welded seam is formed which secures the two webs to each other at the region of the weld thereby forming a curved surface; and
(e) compressing the first web using a blunt rotary cutter so that a cold-weld is formed which secures opposing surfaces of the web to each other in the region of the weld thereby forming a curved surface, said web(s) being compressed along at least three parallel lines to form at least two cords of circular or oval cross-section.
The elongate strip may comprise a plurality of removable edge portions in the form of layers of foam following the contour of the curved surface and extending along the length of the strip. Such masking materials may be made by a method comprising the steps of:
(a) providing a first cold-weldable foam web;
(b) providing at least two second cold-weldable foam webs having a thickness and width smaller than that of the first cold-weldable foam web;
(c) adhering said second webs to a surface of the first web with pressure-sensitive adhesive to form parallel strips of said second webs;
(d) compressing said first and second cold-weldable webs using a blunt rotary cutter so that a cold-welded seam is formed which secures the first and second webs together at the region of the weld thereby forming a curved surface, said webs being compressed along at least two parallel lines along the longitudinal axis of the second webs to form at least one cord of circular or oval cross-section; and
(e) applying a pressure-sensitive adhesive to the surface of the first web in the region between the second webs prior to cold-welding or to the surface of the first web of the cord between the second webs after cold-welding.
In a further embodiment the masking material may comprise a primary cord of circular or elliptical cross-section having a strip of pressure-sensitive adhesive coated thereon and a secondary cord parallel to the primary cord releasably secured thereto. The secondary cord may readily be formed simultaneously with the primary cord from a foam web by cold-welding.
Such a masking material may be made by a method comprising the steps of:
(a) providing a cold-weldable foam web;
(b) compressing said foam web using at least one blunt rotary cutter so that a cold-welded seam is formed which secures opposing surfaces of the web to each other at the region of the weld, thereby forming a curved surface, said web being compressed along at least three parallel lines to form at least two cords having a pair of longitudinal weld seams and a circular or oval cross section, two cords being releasably secured by a common weld and having different dimensions; and
(c) applying a stripe of pressure-sensitive adhesive to the web in the region of the cord having the larger dimension prior to cold-welding or to the cord of larger dimension after cold-welding.
In a further embodiment of the invention the masking material may be in the form of an endless elongate strip e.g., a closed curve, such as a circle or ellipse or other shape, e.g., square, hexagon etc. A concentric array of such strips may be formed e.g., by compressing and cold-welding foam, adjacent strips being separable from each other by tearing the weld. Examples of such an array are disclosed in GB-2254811. In use, the user removes sufficient strips which define an aperture having the area of the surface to be coated and the masking material is applied to the surface. After the first coating e.g., primer has been applied, the inner strip is removed and the second coating applied overlapping the first coating.